Masayuki Gon

Planar chiral tetrasubstituted [2.2]paracyclophane: optical resolution and functionalization.

We achieved optical resolution of 4,7,12,15-tetrasubstituted [2.2]paracyclophane and subsequent transformation to planar chiral building blocks. An optically active propeller-shaped macrocyclic compound containing a planar chiral cyclophane core was synthesized, showing excellent chiroptical properties such as high fluorescence quantum efficiency and a large circularly polarized luminescence dissymmetry factor.

Synthesis of Optically Active, X-Shaped, Conjugated Compounds and Dendrimers Based on Planar Chiral [2.2]Paracyclophane, Leading to Highly Emissive Circularly Polarized Luminescence

Optically active, Fréchet-type dendrimers containing an emissive X-shaped π-electron system as the core unit were synthesized. Gram-scale optical resolution and transformations of 4,7,12,15-tetrasubstituted [2.2]paracyclophanes were also carried out. The high-generation dendrons effectively absorbed UV light and transferred energy to the core, resulting in high photoluminescence (PL) from the core. In addition, the dendrons sufficiently isolated the emissive X-shaped conjugated core and bright emission was observed from both thin films and solutions. Intense circularly polarized luminescence (CPL) was observed from the thin film. The dendrimer films exhibited excellent optical properties, such as large molar extinction coefficients, high fluorescence quantum efficiencies, intense PL and CPL, and large CPL dissymmetry factors.

Optically active cyclic compounds based on planar chiral [2.2]paracyclophane: extension of the conjugated systems and chiroptical properties

A series of optically active cyclic compounds based on the planar chiral tetrasubstituted [2.2]paracyclophane core were synthesized to obtain luminescent materials with excellent chiroptical properties in both the ground and excited states. The optical resolution of tetrasubstituted [2.2]paracyclophane was carried out using our previously reported method. The obtained cyclic compounds were composed of the optically active propeller-shaped structures created by the [2.2]paracyclophane core with p-phenylene–ethynylene moieties. The compounds exhibited good optical profiles, with a large molar extinction coefficient (e) and photoluminescence quantum efficiency (Φlum). The emission occurred mainly from the propeller-shaped cyclic structures. This optically active higher-ordered structure provided chiroptical properties of high performance, such as a large specific rotation ([α]D) and molar ellipticity ([θ]) in the ground state and intense circularly polarized luminescence (CPL) with large dissymmetry factors (glum) in the excited state. The results suggest that planar chiral [2.2]paracyclophane-based optically active higher-ordered structures, such as the propeller-shaped cyclic structure, are promising scaffolds for obtaining CPL and that appropriate modifications can enhance the CPL characteristics.

New Types of Planar Chiral [2.2]Paracyclophanes and Construction of One-Handed Double Helices.

New types of planar chiral (Rp )- and (Sp )-4,7,12,15-tetrasubstituted [2.2]paracyclophanes were synthesized from racemic 4,12-dihydroxy[2.2]paracyclophane as the starting compound. Regioselective dibromination and transformation afforded a series of planar chiral (Rp )- and (Sp )-4,7,12,15-tetrasubstituted [2.2]paracyclophanes, which can be used as chiral building blocks. In this study, left- and right-handed double helical structures were constructed via chemoselective Sonogashira-Hagihara coupling. The double helical compounds were excellent circularly polarized luminescence (CPL) emitters with large molar extinction coefficients, good photoluminescence quantum efficiencies, and large CPL dissymmetry factors.

Diarylamino- and Diarylboryl-Substituted Donor–Acceptor Pyrene Derivatives: Influence of Substitution Pattern on Their Photophysical Properties

Dianisylamino donor (D) and dimesitylboryl acceptor (A) substituents were introduced at the 1,6- and 2,7-positions of pyrene to demonstrate that the substitution patterns influence the photophysical properties. The different pictures in orbital interactions between the pyrene core and the D-A substituents led to the outcome that 1,6-substituted pyrene derivative 1 had stronger electron-donating and electron-accepting properties in conjunction with a small HOMO-LUMO gap, as compared to the 2,7-substituted derivative. For these pyrene derivatives, modest (ΦF = 0.2) to strong (ΦF = 1.0) fluorescence was detected in degassed organic solvents; 1 exhibited a typical intramolecular charge transfer (ICT) emission obeying energy-gap law, while 2 displayed a moderate inverse energy-gap law, originating from the different substitution patterns. Although theoretical calculations predicted that both 1 and 2 adopt highly twisted ICT excited states (TICT excited states) even in the gas phase, but practically, it was suggested that the observed photophysical properties could be determined by the extent of twist angle of the TICT-like excited state in accordance with the solvent polarity. Moreover, the bulky D-A substituents inhibit the intermolecular direct π-π interactions, thereby resulting in the bright and moderate solid-state emissions for 1 (ΦF = 0.76) and 2 (ΦF = 0.21), respectively.

Enhancement of Aggregation-Induced Emission by Introducing Multiple o-Carborane Substitutions into Triphenylamine

The enhancement of aggregation-induced emission (AIE) is presented on the basis of the strategy for improving solid-state luminescence by employing multiple o-carborane substituents. We synthesized the modified triphenylamines with various numbers of o-carborane units and compared their optical properties. From the optical measurements, the emission bands from the twisted intramolecular charge transfer (TICT) state were obtained from the modified triphenylamines. It was notable that emission efficiencies of the multi-substituted triphenylamines including two or three o-carborane units were enhanced 6- to 8-fold compared to those of the mono-substituted triphenylamine. According to mechanistic studies, it was proposed that the single o-carborane substitution can load the AIE property via the TICT mechanism. It was revealed that the additional o-carborane units contribute to improving solid-state emission by suppressing aggregation-caused quenching (ACQ). Subsequently, intense AIEs were obtained. This paper presents a new role of the o-carborane substituent in the enhancement of AIEs.

Controllable intramolecular interaction of 3D arranged π-conjugated luminophores based on a POSS scaffold, leading to highly thermally-stable and emissive materials

This manuscript describes the inorganic cubic core as an advantageous scaffold for realizing solid-state emissive materials with high thermal stability. Polyhedral oligomeric silsesquinoxane (POSS) materials having π-conjugated luminophores connected to eight vertices of the POSS core were prepared. In a dilute solution, the π-conjugated luminophores around the POSS scaffold interacted with the neighboring π-conjugated luminophores, resulting in excimer formation. By introducing bulky alkyl chains into the luminophores, the intrinsic luminescent property of the monomer was recovered. In the solid state, interestingly, the π-conjugated luminophores linked to the POSS scaffold exhibited similar optical properties regardless of the existence of the bulky substituents. Emission bands with almost the same shapes in the spectra were obtained from the POSS materials. In addition, high thermal stabilities of the π-conjugated luminophores were detected. Finally, it was demonstrated that the POSS materials presented bright blue emission even beyond 200 °C in the open air. High thermal stabilities and solid-state emissive properties were realized owing to the cubic structure of the POSS core. A new versatile molecular scaffold for thermally-durable optical materials is offered.

Optically Active Phenylethene Dimers Based on Planar Chiral Tetrasubstituted [2.2]Paracyclophane

Optically active phenylethene dimers based on a planar chiral 4,7,12,15-tetrasubstituted [2.2]paracyclophane were synthesized. We succeeded in controlling the molecular motion by binding luminophores in close proximity with the [2.2]paracyclophane scaffold. For example, aggregation-induced emission (AIE)-active luminophores were converted to show intense photoluminescence (PL) even in a diluted solution at room temperature and the resulting compound worked as a single-molecule thermoresponsible material around room temperature. Because of the AIE-active unit, the molecular motion could be easily activated by heating, leading to variable and reversible PL intensity. Furthermore, the π-conjugated systems with the planar chirality of 4,7,12,15-tetrasubstituted [2.2]paracyclophane provided excellent characteristics on circular dichroism (CD) and circularly polarized luminescence (CPL). The obtained dimers showed high CPL performances both in a diluted solution and in an aggregation state. We succeeded in proving that simple molecular designs composed of only carbon and hydrogen atoms could create versatile optical functionalities.

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiazapentacene (DHDAP) units (1) was investigated as the first example of this kind of molecule. The tetramer 1 showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure 1 exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10-3. The absolute configuration of the enantiomers of 1 was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of 1 with SbCl6- counterions. The solutions of enantiopure 12+·2[SbCl6-] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli.

A Highly Efficient Near‐Infrared‐Emissive Copolymer with a N=N Double‐Bond π‐Conjugated System Based on a Fused Azobenzene–Boron Complex

Fused azobenzene-boron complexes (BAzs) show highly efficient near-infrared (NIR) emission from the nitrogen-nitrogen double bond (N=N) containing π-conjugated copolymer. Optical measurements showed that BAz worked as a strong electron acceptor because of the intrinsic electron deficiency of the N=N double bond and the boron-nitrogen (B-N) coordination which dramatically lowered the energy of the lowest unoccupied molecular orbital (LUMO) of the azobenzene ligand. The simple donor-acceptor (D-A) type copolymer of bithiophene (BT) and BAz exhibited intense photoluminescence (PL) in the NIR region both in the dilute solution (λPL =751 nm, ΦPL =0.25) and in the film (λPL =821 nm, ΦPL =0.038). The BAz monomer showed slight PL in the dilute solution, and aggregation-induced emission (AIE) was detected. We proposed that N=N double bonds should be attractive and functional building blocks for designing π-conjugated materials.